Silicon-on-insulator (SOI) substrate and method for manufacturing the same

ABSTRACT

Disclosed are an SOI substrate and a method for manufacturing the same. The SOI substrate comprises a silicon substrate including an active region defined by a field region. The field region includes a first oxygen-ion-injected isolation region having a first thickness and being formed under the active region. The center of the first region is at a first depth from a top surface of the silicon substrate. The field region of the SOI substrate further includes a second oxygen-ion-injected region having a second thickness greater than the first thickness. The second region is formed at sides of the active region and is also formed from a top surface of the silicon substrate. The center of the second ion injected region is at a second depth from the top surface of the silicon substrate. The first and second ion injected regions surround the active region for device isolation. The SOI substrate is formed by implementing two sequential ion injecting processes. Because the isolation of the active regions can be achieved by implementing the ion injecting process using the sacrificial blocking layer pattern, active regions having various shapes can be obtained with simple and less-costly methods.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a silicon-on-insulator (SOI) substrateand a method for manufacturing the same.

2. Description of the Related Art

As semiconductor devices become highly integrated, current leakage at ajunction area undesirably increases the power consumption. Thus, it hasbecome essential for the semiconductor industry to solve this currentleakage problem in order to obtain high-speed and low-powersemiconductor devices.

More particularly, as the channel length of a transistor decreases to adegree of 0.5 μm or less, leakage current and the junction capacitanceof source and drains of a MOS transistor increase, resulting in anincrease of the parasitic capacitance and the power consumption.

In order to overcome such problems, an SOI substrate has been developedto minimize the junction capacitance, the parasitic capacitance and thecurrent leakage.

Various methods for manufacturing the SOI substrate have been known.Generally, two methods are widely used. One of the two methods is calleda separation by implanted oxygen (SIMOX) method where oxygen atoms areinjected to a predetermined depth of a silicon substrate so that theoxygen atoms penetrate into the predetermined depth of the inner portionof the substrate. Then, the substrate is annealed to manufacture an SOIsubstrate. In the other method, an insulating layer is formed on wafers.Then, two pre-fabricated wafers with an insulating layer are attachedand planarized to form an SOI substrate.

The method of manufacturing an SOI substrate by the conventional SIMOXmethod and a method of forming an active region by this method will bedescribed in detail with reference to attached FIGS. 1A-1D.

FIGS. 1A-1D are cross-sectional views for explaining a method ofmanufacturing an SOI substrate and an active region according to theconventional method. The active region is defined by, for example,shallow trench isolation (STI) regions.

Referring to FIG. 1A, a wafer is injected with oxygen ions and isheat-treated to form a buried oxide layer 20, thus forming an SOIsubstrate including a lower substrate 10, an oxide layer 20 and an SOIlayer 30.

Referring to FIG. 1B, a photoresist is coated on the SOI layer 30 andthen is dried to form a photoresist layer. Then, a conventional photoprocess is performed to form a photoresist pattern 42 in order to exposea surface of the substrate, where a field region is to be formed later.

Referring to FIG. 1C, the SOI layer 30 is anisotropically etched, usingthe photoresist pattern 42 as an etching mask, to form an isolationtrench for a field region 34 (FIG. 1D). Then, the photoresist pattern 42is removed to expose an SOI layer pattern as an active region 32.

Referring to FIG. 1D, the field regions 34 defining the active region 32are formed by filling the trench with an insulating material such asUndoped Silicate Glass (USG). Thereafter, a gate insulating layer and agate electrode are formed on the active region 32 and source and drainregions are subsequently formed by ion implanation.

With the SOI substrate, the source and drain regions of the MOStransistor can be completely separated by field regions. Therefore, ajunction capacitance and current leakage can be reduced and high-speedand lower-power-consumption semiconductor devices with improvedinsulation between the devices can be obtained.

Various methods for manufacturing an SOI substrate using SIMOX aredisclosed as follows.

Japanese Patent Laid-Open Publication No. Hei 8-167646 discloses amethod of manufacturing an SIMOX substrate having two or more singlecrystalline silicon thin films having different thicknesses. The SIMOXsubstrate is manufactured by injecting oxygen ions at a predeterminedregion of a single crystalline silicon substrate using a silicon oxidemask and subsequent heat-treatment at high temperatures.

Japanese Patent Laid-Open Publication No. Hei 4-67649 discloses a methodof forming a device isolation region of an SOI substrate. According tothis method, an insulating layer is formed on a semiconductor layer andthen is patterned to form an insulating layer pattern. Thereafter,oxygen ions are implanted into the semiconductor layer, using theinsulating layer pattern as a mask.

However, according to this method, a local oxidation of silicon (LOCOS)or other isolation trench structures should be formed to accomplishadditional device isolation after implementing the oxygen ion injectionand heat treatment to form the SOI substrate. Accordingly, themanufacturing process becomes complicated and costly.

On the other hand, according to the second method of manufacturing theSOI substrate, two wafers on which insulating layers are formed areattached using heat treatment and are then etched back. With thismethod, one wafer is removed through grinding and a high-temperatureheat treatment is needed for the attachment of the wafers. Thus, voidsmight be formed at the contacting portion. In addition, the wafergrinding process is needed and thereby the process becomes complicatedand costly.

SUMMARY OF THE INVENTION

The present invention contemplates a novel SOI substrate structure andan improved method for manufacturing the same. The SOI substrate inaccordance with one embodiment of the present invention comprises asilicon substrate including an active region defined by a field region.The field region includes a first oxygen-ion-injected isolation regionhaving a first thickness and being formed under the active region. Thecenter of the first region is at a first depth from a top surface of thesilicon substrate. The field region of the SOI substrate furtherincludes a second oxygen-ion-injected region having a second thicknessgreater than the first thickness. The second region is formed at sidesof the active region and is also formed from a top surface of thesilicon substrate to a predetermined depth. The center of the second ioninjected region is at a second depth from the top surface of the siliconsubstrate. The first and second ion injected regions surround the activeregion for device isolation. The SOI substrate is formed by performingtwo sequential ion injecting processes. Because the isolation of theactive regions can be achieved by performing the ion injecting processusing the sacrificial blocking layer pattern, active regions havingvarious shapes can be obtained simply and less-costly.

According to one embodiment of the present invention, an SOI substrateis manufactured by using an SIMOX method. The same mask can be used forperforming two sequential oxygen ion injection processes with differentprocess conditions. A heat treatment is then performed to complete anSOI substrate, in which an active region is separated or surrounded by afield region.

For example, to manufacturing an SOI substrate, a sacrificial blockinglayer pattern is formed on a silicon substrate. The sacrificial blockinglayer pattern defines and covers an active region. First oxygen ions areintroduced at a first energy and at a first dose into a surface of saidsilicon substrate, using the sacrificial pattern as a mask, to form afirst oxygen-ion-injected region in the silicon substrate. Second oxygenions are introduced at a second energy and a second dose to form asecond oxygen-ion-injected region in an upper portion of the siliconsubstrate uncovered by said sacrificial blocking layer pattern. Thesecond energy and the second dose are less than the first energy and thefirst dose, respectively. The first and second oxygen-ion-injectedregions form a field region that surrounds and isolates the activeregion.

BRIEF DESCRIPTION OF THE DRAWINGS

The above object and advantages of the present invention will becomemore apparent by describing preferred embodiments in detail withreference to the attached drawings in which:

FIGS. 1A-1D are cross-sectional views for explaining a method ofmanufacturing an SOI substrate and an active region according to aconventional method;

FIG. 2 is a cross-sectional view of an SOI substrate according to oneembodiment of the present invention;

FIGS. 3A-3D are cross-sectional views for explaining a method ofmanufacturing an SOI substrate according to one embodiment of thepresent invention;

FIG. 4 is a top view illustrating an active region and a field region inan SOI substrate according to a first embodiment of the presentinvention;

FIG. 5 is a top view illustrating an active region in an SOI substratemanufactured by a second embodiment of the present invention;

FIG. 6 is a top view illustrating an active region in an SOI substratemanufactured by a third embodiment of the present invention; and

FIG. 7 is a top view illustrating an active region illustrated in FIG.5, for explaining an effect of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention will be explained in more detail with reference tothe attached drawings below.

FIG. 2 is a cross-sectional view of an SOI substrate according to oneembodiment of the present invention.

Referring to FIG. 2, an SOI substrate according to the present inventionincludes a lower silicon substrate 110, a field region 140 including afirst oxygen-ion-injected isolation region 142 and a secondoxygen-ion-injected isolation region 144, and an active region 150formed on the first oxygen-ion-injected isolation region of the fieldregion 140. As can be seen from FIG. 2, the surfaces of the activeregion 150 and of the field region 140 formed on the substrate 110 areco-planar.

The field region 140 includes the first oxygen ion injected isolationregion 142 having the first thickness 141 and the second oxygen ioninjected isolation region 144 having the second thickness 147. Thecenter of the first oxygen ion injected isolation region 142 is at thefirst depth 143 from the top surface of the substrate and the center ofthe second oxygen ion injected isolation region 144 is at the seconddepth 145 from the surface of the substrate. The first and secondion-injected-isolation regions 142 and 144 are symmetric along thecenter axis thereof, and the first thickness 141 is less than the secondthickness 147.

In FIG. 2, the depth and the thickness of each ion injected region andthe thickness of the active region can be varied depending on the typeand the critical dimension of the device. For example, the first and thesecond depth can be the same and are in a range of about 0.07-0.7 μm fora device having a critical dimension of 0.21 μm or less. For the devicehaving the critical dimension of 0.21 μm or less, the second thicknessis about 2-3.5 times of the first thickness. More preferably, the firstthickness is in a range of about 0.04-0.6 μm and the second thickness isin a range of about 0.14-1.4 μm.

In the SOI substrate satisfying the above-described conditions, thecenter portions of the first and the second ion injected regions 142 and144 are next to each other and accordingly, adjacent active regions 150are separated from the side portion to the bottom portion by theinsulating layer.

A method for manufacturing the SOI substrate will be described withreference to attached FIGS. 3A-3D. FIGS. 3A-3D are cross-sectional viewsfor illustrating the method of manufacturing an SOI substrate accordingto one embodiment of the present invention.

Referring to FIG. 3A, a photoresist layer is coated on a wafer 100 andis patterned to form a photoresist pattern 112 to define an activeregion 150. The photoresist pattern 112 is used as a sacrificialblocking layer for differentially injecting ions into the underlyingwafer 100. For this, a layer having a high etching selectivity withrespect to a silicon or silicon oxide layer, for example, a polyimidelayer pattern, an SOG (spin-on-glass) layer pattern can be used besidesthe photoresist layer.

The sacrificial layer is formed to a predetermined thickness so thatoxygen ions pass through the sacrificial layer during the first oxygenion injecting process, while oxygen ions do not pass through thesacrificial layer during the second oxygen ion injecting process.Particularly, the thickness of the sacrificial layer is in a range ofabout 0.05-0.5 μm.

Referring to FIG. 3B, a first oxygen ion injecting process isimplemented using the photoresist pattern 112 and an ion injector. Theoxygen ions are injected into the wafer 100 as an impurity. However, thedepths of ion injection are different depending on the presence or theabsence of the photoresist pattern 112. That is, if a photoresist layeris formed on the entire surface of the wafer, an imaginary ion injectedregion 125 designated by dashed lines would be formed. However, if thephotoresist pattern 112 is formed on a portion of the wafer, then twoion injected regions having a belt shape or the stepped bell shape areformed to different depths, as illustrated. That is, the ions injectedinto the photoresist pattern 112 are partially blocked by thephotoresist pattern 112. Accordingly, a first ion injected region 120 isformed in the silicon substrate 110. An un-injected upper portion 130 ofthe silicon substrate is disposed over the first ion injected region120, as shown in FIG. 3B.

The preferred process conditions for the first oxygen ion injectingprocess and for a device having a critical dimension of 0.21 μm are asfollows. The ion injection is implemented with ionized oxygen at anenergy range of about 60-80 KeV and at a first dose range of about1×10¹⁸-8×10¹⁸ cm². For a different device, different process conditionsshould be applied. For example, for a device having a dimension of about0.14 μm or less, an ion injecting process is performed at an energy ofabout 60 KeV, which is less than the energy required for the devicehaving a critical dimension of 0.21 μm, and at a dosage of about1×10¹⁸-8×10¹⁸ cm².

Referring to FIG. 3C, a second ion injecting process is implementedafter completing the first ion injecting process in order to form deviceisolation layers, i.e., field regions, at the sides of the active region150 and above the first ion injected region 120. The second ioninjecting process is implemented with the sacrificial layer pattern 112to form a second ion injected region 132 at the upper portion of theexposed substrate, on which the sacrificial layer pattern 112 is notformed, and above the first ion injected region 120. The second ioninjecting process is implemented with less energy than the first ioninjecting process in order to form the second ion injected region 132above the first ion injected region 120. Thus, with the formation of thefirst and the second ion injected regions 120 and 132, a region withoutinjected ions is formed at the upper portion of the substrate below thephotoresist pattern 112.

In order to form the second ion injected region 132, ions are notinjected into the upper portion of the substrate under the photoresistpattern 112, but are injected into the upper portion of the substratewhere the photoresist pattern 112 is not formed. That is, the ions areblocked by the photoresist pattern 112 and injection of the ions intothe substrate is prevented where the photoresist pattern 112 is formed,whereas the ions are injected into the upper portion of the substrateand above the first ion injected region 120 where the photoresistpattern 112 is not formed, as shown in FIG. 3C.

The second oxygen ion injecting process is preferably implemented withionized oxygen, at an energy range of less than 20 KeV and at a seconddose range of about 1×10¹⁸-8×10¹⁸ cm². In addition, during the first andthe second ion injecting processes, ions are injected perpendicular tothe substrate. That is, the ion injecting angle is between approximately0° and 10° during the first and second oxygen ion injecting processes.

Referring to FIG. 3D, the photoresist pattern 112 is removed after thefirst and second ion injecting processes. Then, a heat treatment isimplemented under an oxidizing atmosphere to from a buried oxide layerat the lower silicon substrate 110. Accordingly, an SOI substrateincluding a field region 140 and an active region 150 formed above thefield region 140 is manufactured.

The heat treatment is preferably implemented at a temperature range ofabout 1100-1300° C. for about 2-7 hours under an oxidizing atmosphere.The oxidizing atmosphere can be a mixture gas atmosphere of argon andoxygen.

Using the heat treatment, the impurity doped region changes into aninsulating layer of oxide. In addition, the edge portions of theinsulating layer become smooth because of diffusion. Particularly, sincea stress of the wafer itself is concentrated on an interface and thestress is concentrated at the edge portions. Accordingly, theprobability of generating leakage current at the edge portion increases.However, when the edge portions become smooth through the heattreatment, the leakage current can be advantageously prevented.

FIG. 4 is a top view illustrating an active region and a field region inan SOI substrate according to a first embodiment of the presentinvention. As known from FIG. 4, the side portions and the bottomportion of each active region 152 are completely separated from eachother by the filed region 145.

On the active region 152 of the SOI substrate, a gate insulating layer,a gate electrode, and source/drain regions are subsequently formed toform a MOS transistor on the SOI substrate.

FIG. 5 is a top view illustrating an active region in an SOI substratemanufactured by a second embodiment of the present invention and FIG. 6is a top view illustrating an active region in an SOI substratemanufactured by a third embodiment of the present invention. Accordingto the present invention, the shape of the active region can beadvantageously modified by changing the shape of the sacrificial layerpattern. For example, an active region 154 including a main portion 154a and a projected portion 154 b as illustrated in FIG. 5 can beobtained. Otherwise, an active region 156 including projected portionsat the side portions as illustrated in FIG. 6 can be obtained.

In order to manufacture a circuit on which highly integrated chips aremanufactured, periphery circuits of various shapes should bemanufactured. For the manufacture of the periphery circuits, activeregions having various shapes are required. According to the presentinvention, active regions having various shapes can be advantageouslymanufactured by simply changing the shape of the mask pattern.

FIG. 7 is a top view illustrating an active region illustrated in FIG.5, for explaining an effect of the present invention. An advantageobtainable when manufacturing the active region 154 through the methodof the present invention will be described with reference to

FIG. 7. A DRAM device will be exemplified.

A plurality of gate electrodes and bit lines are formed for themanufacture of the DRAM device. A direct contact hole is formed for theconnection of the bit line with an impurity doped region of the gateelectrode and a plurality of buried contact holes are formed for theconnection of the impurity doped region of the gate electrode with acapacitor between the direct contact holes. At this time, as theintegration degree of a device is heightened and the critical dimensionof the device becomes narrow, a separate region such as the projectedportion of the active region as illustrated in FIG. 7 might be formedconsidering a problem of interference with neighboring buried contacthole.

If the active region having the above-described shape is formed througha plurality of process steps according to the conventional method, itcan be undesirably shifted to the region designated by 154′ in FIG. 7.If a direct contact hole 160 is formed at the shifted active region, acontact region is reduced, resulting in an increase of resistance.However, according to the present invention, an active region is formedthrough two sequential ion injecting processing steps and thus theshifting of the active region does not occur.

As described above, an SOI substrate can be simply manufactured byinjecting oxygen ions at a predetermined depth of a wafer followed byheat-treatment according to the present invention.

While the present invention is described in detail referring to theattached embodiments, various modifications, alternate constructions andequivalents may be employed without departing from the true spirit andscope of the present invention.

What is claimed is:
 1. A method for manufacturing an SOI substrate,comprising: forming a sacrificial blocking layer pattern on a siliconsubstrate, the sacrificial blocking layer pattern defining and coveringan active region; introducing first oxygen ions at a first energy and ata first dose into the silicon substrate using the sacrificial blockinglayer pattern as a mask, thereby forming a first injected region underthe entire active region and forming a first portion of a secondinjected region adjacent to the first injected region; and introducingsecond oxygen ions at a second energy and a second dose into the siliconsubstrate above the first portion of the second injected region usingthe sacrificial blocking layer pattern as a mask, thereby forming asecond portion of the second injected region, the second energy and thesecond dose each being less than the first energy and the first dose,respectively, and wherein the first and second injected regions form afield region that surrounds and isolates the active region.
 2. A methodof manufacturing an SOI substrate as claimed in claim 1, wherein thefield region is substantially dumb-bell shaped.
 3. A method ofmanufacturing an SOI substrate as claimed in claim 1, wherein the firstenergy is about 60-80 KeV and the first dose is about 1×10¹⁸-8×10¹⁸ cm².4. A method of manufacturing an SOI substrate as claimed in claim 1,wherein the second energy is less than 20 KeV and the second dose isabout 1×10¹⁸-8×10¹⁸ cm².
 5. A method of manufacturing an SOI substrateas claimed in claim 1, wherein said sacrificial blocking layer patternis one selected from the group consisting of a photoresist pattern, apolyimide layer pattern and an SOG (spin-on-glass) layer pattern.
 6. Amethod of manufacturing an SOI substrate as claimed in claim 1, whereinsaid sacrificial layer is formed to a predetermined thickness such thatoxygen ions pass through said sacrificial blocking layer pattern duringthe introduction of said first oxygen ions, while oxygen ions do notpass through said sacrificial blocking layer pattern during theintroduction of said second oxygen ions.
 7. A method of manufacturing anSOI substrate as claimed in claim 1, wherein a thickness of saidsacrificial blocking layer pattern is approximately 0.05-0.5 μm.
 8. Amethod of manufacturing an SOI substrate as claimed in claim 1, whereinan ion injecting angle is 0° during the introduction of said first andsecond oxygen ions.
 9. A method of manufacturing an SOI substrate asclaimed in claim 1, wherein the introduction of the first oxygen ionsand the introduction of the second oxygen ions are sequential.
 10. Amethod of manufacturing an SOI substrate as claimed claim 1, wherein thethe first portion of the second injected region is formed deeper thanthe first injected region.
 11. A method of manufacturing an SOIsubstrate as claimed in claim 1, further comprising: removing saidsacrificial blocking layer pattern; and forming an insulating layer byoxidizing said first and second injected regions through a heattreatment of said substrate.
 12. A method of manufacturing an SOIsubstrate as claimed in claim 11, wherein said heat treatment isimplemented at a temperature range of about 1100-1300° C. for about 2-7hours using an oxidizing ambient.
 13. A method of manufacturing an SOIsubstrate as claimed in claim 12, wherein said oxidizing atmosphere is agas mixture including argon and oxygen.